> http://www.spamhaus.org/organization/dnsblusage.html
>
> *Definition: "non-commercial use" is use for any purpose other than as part
> or all of a product or service that is resold, or for use of which a fee is
> charged. For example, using our DNSBLs in a commercial spam filtering
> appliance that is then sold to others requires a data feed, regardless of
> use volume. The same is true of commercial spam filtering software and
> commercial spam filtering services.

My toy domains qualify, sure. But they're mostly toys and though I have
thousands of valid(!) addresses at them, they're mainly used to track who is
selling my name. The addresses are effectively tracking cookies.

My work domains (3 ISP's, with a few thousand users especially) do not qualify.

ISP's, even small ones, must pay.

| Use of the Spamhaus DNSBLs by organizations and networks with email traffic
| likely to exceed the Free Use limits, or by ISPs or commercial spam filter
| services, requires a subscription to the Spamhaus DNSBL Datafeed Service,
| a service designed for users with professional DNSBL requirements.

Strip out the commas to make the sentence simpler:
Use of the Spamhaus DNSBLs by organizations and networks ... or by ISPs ...
requires a subscription to the Spamhaus DNSBL Datafeed Service...

When Spamhaus switched to this model, they sent mail insisting I pay, so
they seem to agree with my interpretation.

[Ironically, the ISP's are actually owned by a Non-profit, and one is
a non-profit itself, using revenues from paying customers to subsidize low income
access... but 501c3 status is not mentioned as a distinguisher between commercial
and non-commercial, and it is all a very complicated arrangement to appease
the IRS anyway...)